Data transfer control device

ABSTRACT

A data transfer control device is provided having a plurality of shift registers connected through said multiplexers in a closed loop, a selector connected to the inputs of said multiplexer and for selecting a transfer destination of display data according to a common electrode select signal of a display unit, and a gate for selecting the polarity of the display data to be loaded into said shift registers according to the polarity of common output signals for scanning common electrodes of said display unit.

BACKGROUND OF THE INVENTION

The present invention relates to a data transfer control device adaptable for transferring display data to a liquid crystal drive circuit for directly driving a liquid crystal display unit of a dynamic drive type.

FIG. 1 shows a prior liquid crystal drive circuit with a duty ratio of 1/4 and with 8-segment outputs. In the drive circuit, a closed loop is formed including four 8-bit shift registers 1₀ to 1₃ connected in a cascade fashion, an inverter 2 for AC-driving a liquid crystal display 6 unit to be described later, and a multiplexer 4. An output signal from a parallel/serial converter circuit 3 for converting parallel data into serial data is transferred to the multiplexer (selector) 4.

The multiplexer 4, controlled by a control signal a supplied from a central processing unit (CPU) (not shown), selects the data from the parallel/serial converter circuit 3 and the inverter 2. The shift register 1₀ is connected at the 8-bit output terminals to a latch/driver circuit 5. The latch/driver circuit 5 converts the parallel data derived from the shift register 1₀ into segment signals SEG₀ to SEG₇ for directly driving a liquid crystal display unit 6. The liquid crystal display unit 6 is connected to the output terminals of the latch/drive circuit 5. The 8-segment liquid crystal display 6 displays four figures at the duty ratio of 1/4 under control of common electrode drive signals COM0 to COM3 generated from a common signal generator 7 to specify a segment to be displayed.

A clock signal generator 8 generates clock signals φT and φL and applies them to the shift register 1₀ and the latch/driver 5. The clock generator 8 is made up of a frequency divider 11 and an AND gate 12, as shown in FIG. 4. Fundamental clock signals φ1 and φ2 are generated by another clock signal generator (not shown). The clock signal φ1 is applied to one of the input terminals of the AND gate 12. The clock signal φ2 is applied in an inverted state to the frequency divider 11, and is appplied in a non-inverted state to the shift register 1₀. The signals at different frequencies are applied from the frequency divider 11 to the remaining input terminals of the AND gate 12. The AND gate 12 responds to the clock signal φ1 to produce the clock signal φL for transferring to the latch/driver 5. One clock signal φL is produced every time eight pulses of the clock signal φT are produced.

FIG. 5 shows an example of the common signal generator 7 for generating common electrode drive signals COM0 to COM3. The common signal generator 7 includes p-channel MOS transistors TR7 and TR8 and n-channel MOS transistors TR9 and TR10, all of which have the current paths which are connected in series between power source terminals VD and VL. Generator 7 also has p- and n-channel MOS transistors TR11 and TR12 connected in parallel between a node coupled to a resistor R2 and a resistor R3 and a node coupled to the MOS transistor TR8 and the MOS transistor TR9. NAND gate 121 applied with a first common electrode select signal d0 and a blanking signal BLK.

The gates of the MOS transistors TR7 and TR10 are connected through an inverter 122 to a control terminal WCLT. The gates of the MOS transistors TR8 and TR12 are connected together to the output terminal of the NAND gate 121. The gates of the MOS transistors TR9 and TR11 are connected through an inverter 124 to the output terminal of the NAND gate 121 having as inputs a first common electric signal do and a blanking signal BLK.

A 0-th common electrode drive signal COM0 is produced from a node between the MOS transistors TR8 and TR9. The circuit arrangements of the remaining circuit sections 125, 126 and 131 are each substantially the same as that of the circuit section 127. These circuit sections 125, 126 and 131, respectively, produce the first to third common electrode drive signals COM1 to COM3 in response to the output signals from NAND gates 128, 129 and 132 which receive at the first input terminals a blanking signal BLK and at the second input terminals the first to third common electrode select signals d1 to d3.

FIG. 6 shows a time-division control circuit in which four D-type flip-flops 21₀ to 21₃ connected in a cascade fashion make up a ring counter. In the figure, the Q output terminal of the flip-flop 21₀ is connected to a D input terminal of the succeeding stage flip-flop 21₁ of which the Q output terminal is connected to the D input terminal of the succeeding flip-flop 21₂. The Q output terminal of the flip-flop 21₂ is connected to the D input terminal of the flip-flop 21₃. The Q output signals from the flip-flops 21₀ to 21₃ are sent as common electrode select signals d0 to d3. The signals d0 to d2 of these common electrode select signals are supplied through an OR gate 22 and an inverter 25 to the D input terminal of the flip-flop 21₀.

The clock signal φL is applied to the clock terminals CK of the flip-flops 21₀ through 21₃ and a clear signal is applied to the clear terminals CL of the same flip-flop.

The time division control circuit under discussion is further provided with a circuit for generating a PHASE signal and a polarity inverting signal W. An output signal CTL of the OR gate 22 is applied to one of the input terminals of a XNOR gate 24. The output signal from the XNOR gate 24 is produced as the PHASE signal and is also applied to a D-type flip-flop 23. The clear terminal CL and the clock terminal CK of the flip-flop 23 are supplied with the clear signal and the clock signal φL, respectively. The polarity inverting signal W is derived from the Q output terminal of the flip-flop 23 and is applied to the other input terminal of the XNOR gate 24.

FIGS. 7A to 7F show timing diagrams of input signals applied to the time division control circuit and output signals produced from the same circuit. At the timing of the clock signal φL shown in FIG. 7B, the CTL signal shown in FIG. 7D, after being inverted by the inverter 25, is applied to the D input terminals of the flip-flops 21₀ through 21₃, thereby to provide the signals d0 to d3 shown in FIG. 7C. The CTL signal is at a high level so long as the signals d0 to d2 are logic "1". When the signal d3 is logic "1", the signals d2 through d0 are all logic "0". These signals are applied to the OR gate 22, so that the CTL signal as the output signal from the OR gate 22 is at low level, as shown in FIG. 7D. As a result, the CTL signal at a low level is applied to one of the input terminals of the XNOR gate 24 and the polarity inverting signal at low level, after being inverted, is applied to the other input terminals of the XNOR gate 24. Therefore, the XNOR gate 24 produces the PHASE signal at high level.

The output signal from the XNOR gate 24 is further latched in the flip-flop 23. When any one of the common electrode select signals d0 to d2 is at high level, the CTL signal is at high level. Accordingly, the XNOR gate 24 produces a PHASE signal at high level, so that the PHASE signal as shown in FIG. 7E is obtained. As a result, the inverting signal W becomes a signal as shown in FIG. 7F which is the PHASE signal delayed a fixed time. The common electrode select signals d0 through d3 are applied to the common electrode drive signal generator circuit of FIG. 5, thereby forming the common electrode drive signals COM0 to COM3 as shown in FIGS. 7G through 7J.

FIG. 2 shows another example of a prior art liquid crystal drive circuit. In this example four shift registers 1₀ to 1₃ are connected in a cascade fashion. Multiplexers 4₀ through 4₃ are provided so as to write data of 4 bits from the CPU to the shift registers 1₀ to 1₃. One-bit signals are applied to each of the input terminals of these multiplexers 4₀ through 4₃. The output signals from the shift register 1₃ are applied to the other input terminal of the multiplexer 4₀ ; the output signal from the shift register 1₂ to the other input terminal of the multiplexer 4₁ ; the output signal from the shift register 1₁ to the other input terminal of the multiplexer 4₂ through the inverter 2; the output signal from the shift register 1₀ to the other input terminal of the multiplexer 4₃.

The shift register 1₀ is connected through the latch/driver circuit 5 to the liquid crystal display unit 6. The fundamental clock signal φT is applied to the shift registers 1₀ through 1₃ and the clock signal φL is supplied to the latch/driver circuit 5. The common electrode drive signals COM0 to COM3 are applied from the common electrode drive signal generator 7 to the liquid crystal display 6. A control signal al for selecting the data from the CPU or the data from the shift registers 1₀ through 1₃ is applied to the multiplexers 4₀ to 4₃.

FIG. 8 is a block diagram illustrating an interconnection of the liquid crystal drive circuit shown in FIG. 2 with a microcomputer (CPU) 31 for supplying display data to the liquid crystal drive circuit. In the figure, the common electrode drive signal generator 32 transfers a display data transfer ready signal l shown in FIG. 10G to the CPU 31 and a transfer data inverting control signal K to the multiplexer 33. Further, the circuit 32 transfers the common electrode drive signals COM0 to COM3 to the liquid crystal (LC) display 6, through transfer lines 35.

FIG. 9A illustrates a figure including eight segments a to h of a digit used in the display unit 6. FIG. 9B shows a format of a segment specifying buffer containing fields for specifying the data representing the segments of the figure shown in FIG. 9A. Since the present examples use a 4-bit microprocessor, two stages of 4-bit segment specifying buffer are used for specifying the 8-segment data. As shown, bit 0 corresponds to the common electrode drive signal COM0; bit 1 to the drive signal COM1; bit 2 to the drive signal COM2; bit 3 to the drive signal COM3.

As shown in FIGS. 10A to 10J, when the common electrode select signals d0 to d2 are at low level and the select signal d3 is at high level, the data transfer ready signal l shown in FIG. 10G is at high level. As a result, the data transfer signal as shown in FIG. 10I is produced. The CPU 31 acknowledges the reception of the transfer ready signal l, and at the time of the high level of the signal d3, transfers the data corresponding to the signal COM0 to the shift register 1₀, the data corresponding to the signal COM1 to the shift register 1₂, the data corresponding to the signal COM2 to the shift register 1₂, and the data corresponding to the signal COM3 to the shift register 1₁. Thus, in the prior liquid crystal drive circuit, a fixed timing relationship is established between the common electrode drive signals COM0 to COM3 and the transfer data. This fixed timing relationship frequently hinders correct LC display operation. In other words, there is poor flexibility in setting up the transfer timing of the display data. Therefore, when the frame frequency shown in FIG. 10A is 100 Hz, the CPU must wait a maximum of 10 ms till data transfer is permitted.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention relates to a data transfer control device with improved flexibility in setting up a transfer timing of data and an improved transfer efficiency of data.

In a data transfer control device according to the present invention, a selector for selecting a transfer port of the display data is provided in display data transfer lines connecting to the multiplexers. With the provision of the selector, the data transfer is allowed at a desired timing. Therefore, the data transfer processing is relatively independent of the program, thereby improving data transfer efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and features of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which:

FIGS. 1 and 2 are block diagrams of prior art liquid crystal drive circuits;

FIGS. 3A through 3C include timing diagrams illustrating sequential operations of the liquid crystal drive circuits of FIGS. 1 and 2, in which FIG. 3A shows a waveform of a fundamental timing signal φ1, FIG. 3B a waveform of a clock signal φL for display latch, and FIG. 3C a waveform of a clock signal φT for shifting shift registers;

FIG. 4 is a schematic block diagram of a circuit for generating the clock signals φL and φT shown in FIGS. 3B and 3C;

FIG. 5 is a circuit diagram of a common electrode drive signal generator circuit used in the circuit shown in FIGS. 1 and 2;

FIG. 6 is a circuit diagram of a time division control circuit necessary for the liquid crystal drive circuits shown in FIGS. 1 and 2;

FIGS. 7A through 7J include timing diagrams illustrating a set of waveforms of signals formed by a time division control circuit shown in FIG. 6, in which FIG. 7A shows a waveform of a clock signal φT for shifting shift registers, FIG. 7B a waveform of clock signal φL for a display latch, FIG. 7C waveform of common electrode select signals d0 to d3 produced from the time division control circuit shown in FIG. 6, FIG. D a waveform of a CTL signal produced from the same circuit, FIG. 7E a waveform of a polarity inverting preparatory signal PHASE, FIG. 7F a waveform of a polarity inverting signal W, and FIGS. 7G to 7J waveforms of common electrode drive signals COM0 to COM3;

FIG. 8 is a block diagram of a prior circuit arrangement for driving the liquid crystal drive circuit shown in FIG. 2 by a microcomputer;

FIG. 9A illustrates a figure made up of eight segments a to h located at a digit space of the liquid crystal display;

FIG. 9B shows a format of a segment specifying buffer for specifying the data representing segments of the figure;

FIGS. 10A through 10J include timing charts illustrating a transfer state of display data in which FIGS. 10A to 10D illustrate common electrode select signals d0 to d3, FIG. 10E a waveform of a polarity inverting signal, FIG. 10F a waveform of a COM0 signal, FIG. 10G a waveform of a transfer ready signal 1, FIG. 10 a waveform of a transfer data inversion control signal K, FIG. 10I a waveform of a transfer data signal from a CPU, and FIG. 10J, a waveform of a display data signal;

FIG. 11 shows the interrelation of common output signals and shift registers 1₀ to 1₃ in the FIG. 8 circuit;

FIG. 12 shows a circuit diagram of an embodiment of a data transfer device according to the present invention;

FIGS. 13A to 13I show waveforms of signals used in the FIG. 12 circuit, in which FIG. 13A shows a polarity inverting signal, FIGS. 13B to 13E waveforms of common electrode select signals d0 to d3, and FIGS. 13F to 13H waveforms of common electrode drive signals COM0 to COM3; and

FIGS. 14A through 14F are timing charts illustrating a transfer state of display data, in which FIGS. 14A to 14D shows waveforms of segment electrode select signals, FIG. 14E a waveform of a transfer data signal from a CPU, and FIG. 14F a waveform of a display data signal.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 12 shows an embodiment of a data transfer control device according to the present invention. In the figure, like numerals are used to indicate like portions in FIG. 2. In the present embodiment, a selector 42 for selecting a transfer destination of the data transferred to the shift registers 1₀ to 1₃ is provided in the display data transfer path from the data bus 41 of the CPU to the multiplexers 4₀ to 4₃. The selector 42 is made up of groups of gates 47₀ to 47₃, 48₀ to 48₃, 49₀ to 49₃, and 50₀ to 50₃. A display data signal is applied to the gates 50₀, 49₀, and 48₀. The inverted signal D₀ from an inverter 43 coupled at the input with the signal D₀ is supplied to the gate 47₀. A signal D1 is applied to the gates 49₁ to 48₁ and its inverted signal D₁ derived from an inverter 44 is applied to the gates 50₁ and 47₁. A D₂ signal is applied to the gate 48₂ and its inverted signal D₂ from an inverter 45 is applied to the gates 50₂, 49₂ and 47₂. An inverted signal D₃ from an inverter 46 is applied to the gates 50₃, 49₃, 48₃ and 47₃. The gates 47₀ (D₀), 48₃ (D₃), 49₂ (D₂) and 50₁ (D₁), the gates 47₁ (D₁), 48₀ (D₀), 49₃ (D₃) and 50₂ (D₂), the gates 47₂ (D₂), 48₁ (D₁) and 49₀ (D₀), 50₃ (D₃) and the gates 47₃ (D₃), 48₂ (D₂), 49₁ (D₁) and 50₀ (D₀) constitute first to fourth gate groups, respectively.

As shown, a common electrode select signal d0 is applied to the 2nd gate group; a common electrode select signal d1 to the 3rd gate group; a common electrode select signal d2 to the 4th gate group; and ANDed signal of these signals d0 to d2 (passed through a three-negative input AND gate 51) is applied to the first gate group. The multiplexer 4₀ is made up of three AND gates 52₀ to 52₂ and an OR gate 56₀ connected at the input to these three AND gates. The remaining multiplexers 4₁ to 4₃ have each a similar circuit arrangement to that of the multiplexer 4₀. The output signals from these multiplexers 4₀ to 4₃ are applied to the shift registers 1₀ to 1₃, respectively.

An output signal from a shift register 1₀ is applied through an inverter 2 to one of the input terminals of the AND gate 53₂ ; an output signal from the shift register 1₁ to one of the input terminals of the AND gate 54₂ ; an output signal from the shift register 1₂ to one of the input terminals of the AND gate 55₂ ; an output signal from the shift register 1₃ to one of the input terminals of the AND gate 52₂. The data signals from the 1st to 4th gate groups are respectively applied to first input terminals of the AND gates 52₁, 53₁, 54₁ and 55₁, and through inverters 61₀ to 61₃ to first input terminals of the AND gates 52₀ to 55₀.

A display/transfer signal m is applied to the second input terminals of the AND gates 52₂ to 55₂, through an inverter 57. An output signal from a two-negative input AND gate 60 is applied to the second input terminal of the AND gates 52₁ to 55₁. An output signal from a two-negative input AND gate 59 is applied to the AND gates 52₀ to 55₀. The display/transfer signal m is applied through the inverter 57 to the first input terminals of AND gates 59 and 60.

When the display/transfer signal m is logic "0", a data display is going on, while when it is logic "1", a data transfer is going on. The polarity inverting preparatory signal PHASE is directly applied to the second input terminal of the AND gate 60, and applied through an inverter 58 to the second input terminal of the AND gate 58. With such a circuit arrangement, when the signal m is logic "1" and the signal PHASE is logic "0", if the data is transferred at the timing of the signal d3, the gates of the first gate group are enabled to allow the data D₀ to go to the shift register 1₀, the data D₃ to go to the shift register 1₁, the data D₂ to go to the shift register 1₂, and the data D₁ to go to the shift register 1₃.

At the other timings d0 to d2, the data are transferred to the shift registers 1₀ to 1₃ in a similar process. When the signal m is logic "1" and the signal PHASE is logic "1", if the data is transferred at the timing of the signal d3, the related logics operate to allow the data D0 to go to the shift register 1₀, the data D3 to go to the shift register 1₁, the data D2 to go to the shift register 1₂, and the data D1 to go to the shift register 1₃.

Relationships between the registers and the data loaded into them in such operations are tabulated in FIG. 13. When the signal m is logic "0", the AND gates 52₂ to 55₂ in the multiplexers 4₀ to 4₃ are enabled and the remaining AND gates of the multiplexers are disabled through the AND gates 59 and 60. The result is the formation of a closed loop of shift registers 1₀ to 1₃. When the output signal from the AND gate 60 is logic "1", the gates 52₁ to 55₁ are enabled to allow the inverted signal WI1 to WI4 to go to the shift registers 1₀ to 1₃. When the output signal from the AND gate 59 is logic "1", the AND gates 52₀ to 55₀ pass the signals WI1 to WI4 to the shift registers 1₃ to 1₀ through inverters 61₀ to 61₃. The AND gates 59 and 60 are provided for loading signals with the opposite polarity to that of common electrode drive signals COM0 to COM3 into the shift registers 1₀ to 1₃. The subsequent data inversion is made by the inverters in the shift register loop. As seen from FIG. 13, the display data regularly changes with the change of the signals d0 to d3. Accordingly, the signals d0 to d3 are applied to the selector 42 and the data corresponding to those signals are loaded into the shift registers 1₀ to 1₃. 

What we claim is:
 1. A data transfer control device having an input terminal for receiving constant-formatted data and an output terminal for connection to a display having common electrodes, said data transfer control device comprising:a plurality of shift registers for storing data and providing output signals to said output terminal; means for receiving a common electrode selecting signal; selector means, coupled to said input terminal and said common electrode selecting signal means, for receiving said constant-formatted data at said input terminal, for changing the arrangement of said constant-formatted data in accordance with said common electrode selecting signal, said selector means comprising a plurality of outputs for outputting said data with changed arrangements to a plurality of multiplexers; and; means for receiving a mode selection signal; wherein each one of said plurality of multiplexers is coupled to said mode selection signal receiving means and to a different one of said selector means outputs, and is further coupled to an input of a different one of said plurality of shift registers, said plurality of multiplexers including means, responsive to said mode selection signals, for either supplying said constant-formatted display data from said selector means to said shift registers or shifting the stored data in said shift registers in a closed loop.
 2. A data transfer control device according to claim 1, wherein said selector means includes means for determining the polarity of the constant-formatted data to be supplied to said shift registers.
 3. A data transfer control device according to claim 1, wherein said selector means includes means for inverting said constant formatted data. 